Make-up brushes accumulate oils from the skin, as well as the pigments, waxes, and emollients in make-up. These ingredients and oils, do not dissolve in water (they're designed that way so they don't come off easily), so they require the "like dissolves like" theory....oils dissolve oil.

The olive oil will dissolve and loosen all the make-up from the fibers of the brush, so you can just suds em' up, and they're good as new.

You can also use olive oil as an eye make-up remover...great for your lashes and skin as well...and considering you can buy a gallon of olive oil for about $25 bucks....it'll be the cheapest make-up remover you'll ever have.